We had this legacy Solaris on SPARC service, 3 layer, sounds similar architecture but more servers, cores, fairly good amount of storage. Recently we had issues with Oracle pegging CPU cores and there's a 2 year late project to replace it with almost 200 servers (because growth and shit.)
I replaced it with 2 containers (for the App itself) running on a 2 VM cluster mounting from our ceph cluster (standard enterprise service) and a containerized postgresql cluster (standard enterprise service). Two week hack-a-thon with 3 developers and myself. We did rewrite the application from ancient C++ to Go.
The App containers are expandable, but in the 60 days in production we haven't had to expand them. The postgresql cluster didn't have any noticeable increase and same with ceph cluster. We did discuss doing a microservices architecture, but that only makes sense in certain circumstances and this was not it.